In general, proper carpet maintenance involves regular vacuuming and periodic cleaning to remove soil by methods such as hot water extraction, shampooing, bonnet cleaning, foam cleaning, etc. Some of the soil is loosely found between carpet fibers while other soil is held upon the carpet fibers by some means such as electrostatic forces, van der Waals forces, or oil bonding. Still other soil is mechanically trapped by carpet fibers. Regular vacuuming is essential as it removes some of the loose soil that damages the fibers. Vacuuming maintains the surface appearance of a carpet and keeps the level of soil in the pile at an acceptable level. Vacuuming removes only particulate soil and some unbound or loosely bound surface dirt; therefore, other methods of cleaning are periodically required to improve the appearance of the carpet. Wet cleaning methods are better for removing oils, greases, bound dirt, and other forms of matter that cause soiling on carpet. These methods are often used by professional cleaners and trained personnel.
One type of surface maintenance machine for carpet cleaning is referred to as a bonnet cleaner. Bonnet cleaners employ an absorbent bonnet or pad (hereinafter referred to as the “pad”) attached to a rotary driver for rotating the pad about an axis generally perpendicular to the carpet surface. Cleaning liquid is sprayed directly onto the carpet followed by the rotating pad used to agitate the carpet and transfer soil from the carpet onto the bonnet, i.e., the pad. Since the pad is commonly two-sided, the pad may be reversed once one side of the pad gets soiled to a selected level. The pad may be periodically replaced and later cleaned depending upon the application and wear characteristics of the pad.
The soil transfer process of the bonnet cleaners may be characterized as a “circular engagement process” since the pad rotates relative to the carpet surface. The method employed by bonnet cleaners does have the advantage of being fast drying if a relatively small amount of cleaning liquid is employed. However, limitations of bonnet cleaners include transferring soil from soiled areas to a relatively cleaner area, leaving much of the cleaning fluid in the carpet, and having the potential to damage the carpet. With respect to the latter, some carpets, particular twisted ply variations, may be damaged by aggressive engagement with the rotating pad. Additionally, the bonnet cleaning process is a relatively labor intensive process since the pad requires frequent soil monitoring and frequent removal of soiled pads.
Yet another limitation of bonnet cleaners is the relatively uncontrolled use of cleaning liquid in the carpet cleaning process as some areas of the carpet may receive more cleaning liquid spray than other areas. Reliance on operator spraying of cleaning liquid to the carpet surface may result in overwetting of some areas and underwetting of other areas.
Another type of surface maintenance machine intended for carpet cleaning is referred to as an “extractor machine.” Extractor machines are commonly used for deep carpet cleaning. In general, an extractor is a transportable self-contained device which (i) sprays cleaning liquid directly onto the carpet to create a wetted carpet portion, (ii) agitates the wetted portion with a brush, and (iii) removes some of the cleaning liquid and soil in the carpet through a vacuum system. Generally, in the extraction process a relatively large quantity of cleaning liquid is applied on the carpet. While the vacuum system recovers a portion of the applied cleaning liquid, a significant portion is retained by the carpet. As a consequence, carpet drying times are substantially longer than in the bonnet cleaning process. Excessive carpet wetting may promote the growth of fungus and/or bacteria within the carpet. Additionally, carpet overwetting may also cause surface stains to appear or reappear as underlying soil or stains migrate from the bottom of the carpet to its surface. Additionally, extractors are generally limited to a single operational direction as the steps of wetting, agitation, and vacuuming are sequentially performed. As a result, extractor machines may be difficult to maneuver in some environments, i.e., complex floor layouts.